When I first looked at doing this (I had no need for it in our site), I thought it might require changing the Master Page, but I found out it was much easier.
All you need to do is go to Central Admin for your site app. then, under
System Settings>Farm Management>Manage Farm Features
you will find the following feature:
Social Tags and Note Board Ribbon Controls
Now – deactivate it. You’re done!
All Things DotNet Discussed – Winforms/ASP.Net/SharePoint/WPF